I am doing lots of landscape and outdoor photography and one of the biggest drawbacks is that I have to carry heavy dslr gear together with an already heavy backpack.
So I was thinking about a paradigm shift and going down to a smaller system.

I guess that losing width at the wide end of the focal range is the biggest fear I have at this point. I need and love the ultra wide angle. Currently the EF-S 10-22 is my favourite outdoor lens. I know that I can't expect such extreme angles at a M4/3 but is there at least some lens available with considerable wide angle performance?

Other necessary features for landscapes would be the ability to attach filter systems or at least a CPL filter. Bulb mode and manual exposure features + bracketing would be important as well.
What about remote shutters? Is there something available?

Can't say I've been doing what I would call serious landscape shooting with it, but I did take it as a second body while on a landscape trip. I was using it mostly while walking because I didn't want to take the DSLR out of the bag until I had reached my destination. So, I was using it handheld and without any filter. That said, the results were pretty good. Not quite as good as what I could get with my DSLR (especially the dynamic range), but not very far either. Certainly much better than what I would get from a compact camera. So good, actually, that I'm considering doing exactly what you're saying: taking only the m4/3 camera on longer hikes.

To answer you questions more specifically (my answers are for the Olympus Pen E-P1 but probably valid for other m4/3 models):

Can you attach filters? Both of my lenses (oly 14-42mm and panny 20mm) have filter threads. I haven't tried them but see no reason why you couldn't use a CPL.

Is there a bulb mode/manual mode? Yes, and both are easily accessible.

Is there autobracketing? Yes, but buried in the menus.

Can you use a remote shutter? Olympus and some third party manuf. make some but I haven't tried them.

Ultra wide angle options: Both Olympus and Panasonic make ultra wide angle zooms for the m4/3 cameras. Panasonic's is a 14-28mm equiv, while oly's is an 18-36mm equiv. Both are said to be good, with panasonic's more expensive offer being optically better. I haven't tried either.

As you might have guessed by now, I believe a m4/3 kit can be a very decent option for landscape photography. Not quite as good as a DSLR, but I don't think the difference is that big. And it would certainly be much smaller and lighter.